This is a resubmission of the application Implementing School Wide PBS in Middle Schools. The proposed project would experimentally evaluate the impact of school wide Positive Behavior Support (PBS) on the behavior and development of early adolescents in middle schools. Middle schools are the dominant form of education for early adolescents in the United States. However, their most common practices for addressing students'behavioral development appear to be counterproductive, especially for students with aggressive and disruptive behavior problems. Existing evidence indicates that inadequate behavior management practices that are characteristic of middle school environments contribute to higher levels of aggressive and disruptive behavior and to higher levels of peer harassment and rejection. These factors, in turn, may contribute to the formation of deviant peer groups and deviant peer group membership is a well-established influence on the development of multiple problems in adolescence, including antisocial behavior, substance use, high risk sexual behavior and depression. Positive Behavior Support (PBS) is a school wide, comprehensive system for promoting positive social behavior and limiting aggressive and disruptive behavior in all the settings within the school. Existing evidence in elementary and middle schools suggests that PBS has a powerful impact in reducing inappropriate behavior and promoting positive social behavior. However, despite a growing use of PBS, it has not been evaluated in a randomized controlled trial. Thus, we propose to randomize 36 middle schools to receive extensive training and consultation in PBS implementation or simply a one-day workshop on PBS. The project will test a model of the hypothesized influence of school behavior management practices on aggressive behavior, peer harassment and rejection, the formation of deviant peer groups, and the subsequent development of antisocial behavior, substance use, high risk sexual behavior and depression. The research will contribute to our basic understanding of early adolescent development at the same time that it provides a rigorous test of a highly promising preventive intervention. The specific aims for the project are to Evaluate the effects of the PBS intervention in a group-randomized trial, Assess the differential impact of intervention fidelity on targeted outcomes, Test a model of the influence of middle school discipline practices on the development of adolescent problems, Assess the maintenance of the PBS intervention after termination of training and technical assistance, and Assess the relationship of Office Discipline Referral data to adolescents'reports of their engagement in diverse problems.